This application claims the benefit of Japanese Patent Application No. 2000-314292, filed Oct. 13, 2000, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein.
This invention relates to reflection photomasks that are used for integrated circuit manufacturing, and more particularly to reflection photomasks that are used with extreme ultraviolet radiation for integrated circuit manufacturing and methods of manufacturing and using the same.
As integration densities of integrated circuit devices continue to increase, it may become increasingly difficult to fabricate fine linewidths using conventional photomasks. Thus, for example, exposure of a pattern size of about 250 nm may be performed using Deep UltraViolet (DUV) radiation at, for example, 248 nm. Moreover, other DUV technologies, which can use a radiation source of shorter wavelength than about 193 nm, can decrease the pattern size to between about 100 and about 130 nm. In order to expose pattern sizes of less than about 100 nm, for example pattern sizes of about 5 to about 70 nm, exposure wavelengths in the Extreme UltraViolet (EUV) region, also referred to as the xe2x80x9csoft X-ray regionxe2x80x9d, may be used. EUV radiation may cover wavelengths of between about 10 nm to about 14 nm, for example about 13.4 run to about 13.5 nm.
EUV exposure may use a reflection photomask in contrast with conventional transmission photomasks, since many materials may have a large optical absorptivity in the EUV region. In general, an EUV reflection photomask may be obtained by forming a pattern in an absorber, which can absorb EUV radiation, on a reflection mirror having large reflectivity in the EUV region. Thus, the regions in which the surface of the reflection mirror is covered with the absorber pattern become absorption regions, and the regions in which the surface of the reflection mirror is exposed become reflection regions. The reflection layer generally comprises a plurality of alternating films comprising first and second materials, such as Mo/Si and/or Be/Si.
FIG. 11 shows an embodiment of a conventional reflection photomask 110. A reflection layer 112 comprising a multi-layer film is formed on a substrate 111 such as a silicon and/or glass substrate. An absorber pattern 113 for EUV rays which comprises, for example, a TaN film having a predetermined pattern, is formed on the reflection layer 112.
However, when directly forming the absorber pattern 113 on the reflection layer 112, as shown in FIG. 11, the exposed portion of the surface of the reflection layer 112 may be etched and/or damaged, during patterning (etching) of the absorber. This damage may reduce the reflectivity.
As shown in FIG. 16, the above defects may be reduced or eliminated using Focused Ion Beams (FIB). For example, in FIG. 16, an etching residue portion 113a in the absorber pattern at the left side and a damaged portion 113b in an adjacent absorber pattern may be generated during patterning of the absorber pattern 113. FIB can locally remove only the residue portion 113a by an etching operation. The damaged portion 113b of the pattern also may be locally traced by the absorber and buried by irradiating the FIB at a predetermined gas atmosphere. This process often is referred to as a mask repair process. Unfortunately, however, in the structure shown in FIG. 11, the FIB irradiation itself can damage the surface of the reflection layer during the mask repair process.
Damage can be reduced when patterning the absorber as described in Hoshino et al., Process Scheme for Removing Buffer Layer on Multilayer for EUVL Mask, Proceedings of the SPIE, Vol. 4066, July 2000, pp. 124-130, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. For example, as shown in FIG. 12 herein, a buffer layer 123 comprising an SiOx film is formed under an absorber pattern 124 in a photomask 120. When the photomask 120 is manufactured, a reflection layer 122 comprising a multi-layer film is formed on a substrate 121, as shown in FIG. 13A. A buffer layer 123a is formed on the reflection layer 122, as shown in FIG. 13B. An absorber layer 124a is formed on the buffer layer 123a, as shown in FIG. 13C.
As shown in FIG. 13D, the absorber pattern 124 is formed by patterning the absorber layer 124a by photolithography. A two stage etching method is used for patterning. First, dry etching is performed. In particular, the buffer layer 123a is etched after the absorber layer 124a, as shown in FIG. 13E. Etching is stopped in a state where the buffer layer 123a still remains. Wet etching is then performed. In particular, the surface of the reflection layer 122 is exposed by completely removing the remaining buffer layer 123a, as shown in FIG. 13F. Accordingly, it is possible to reduce the amount of over-etching of the surface of the reflection layer by using a wet etching process having etching selectivity higher than that of the dry etching.
Damage also can be reduced when pattering the absorber as described in Mangat et al., EUV Mask Fabrication With Cr Absorber, Proceedings of the SPIE, Vol. 3997, July 2000, pp. 76-82, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. For example, as shown in FIG. 14 herein, in a photomask 140, a buffer layer 144 comprising an SiON film is formed under an absorber pattern 145. Furthermore, an etch stop layer 143, comprising a Cr film of about 10 nm in thickness, is formed under the buffer layer 144. When the photomask 140 is manufactured, a reflection layer 142 comprising a multi-layer film is formed on a substrate 141, as shown in FIG. 15A. An etch stop layer 143a is formed on the reflection layer 142, as shown in FIG. 15B. A buffer layer 144a is formed on the etch stop layer 143a, as shown in FIG. 15C. An absorber layer 145a is further formed on the buffer layer 144a, as shown in FIG. 15D.
After forming the absorber pattern 145 by patterning the absorber layer 145a by photolithography, as shown in FIG. 15E, the buffer layer 144a is etched, as shown in FIG. 15F. Since the etching selectivity of the SiON film can be high with respect to Cr, etching of the buffer layer 144a can stop at the surface of the etch stop layer 143a. As shown in FIG. 15G, the surface of the reflection layer 142 is exposed by removing the etch stop layer 143a. Accordingly, the surface of the reflection layer may not be over-etched during etching of the buffer layer by using the etch stop layer.
Unfortunately, the Hoshino et al. technique may use a complicated two-stage etching. It may be difficult to control the dry/wet etching process and the surface of the reflection layer may be damaged.
Moreover, the Mangat et al. technique also may complicate fabrication due to the etch stop layer. It may be possible to prevent the surface of the reflection layer from being over-etched during etching of the buffer layer by forming the etch stop layer. However, the surface of the reflection layer may be over-etched when the etch stop layer is removed subsequently. For example, when the etch stop layer comprising Cr remains on the reflection region, the etch stop layer may need to be removed since the optical absorptivity of the Cr film is strong and reflection on the surface of the reflection layer may be reduced. However, since etching selectivity of Cr with respect to the surface of the reflection layer may be low, the surface of the reflection layer may be over-etched.
Reflection photomasks, according to some embodiments of the invention, add a buffer layer comprising at least one Group VIII metal between the reflection layer and the absorber pattern that is configured to absorb extreme ultraviolet rays therein. In particular, some embodiments of reflection photomasks according to the invention include a substrate and a reflection layer comprising a plurality of alternating films comprising first and second materials, respectively, on the substrate. A buffer layer comprising at least one Group VIII metal is provided on the reflection layer opposite the substrate. An absorber pattern comprising material that is patterned in a predetermined pattern and that is configured to absorb extreme ultraviolet rays therein, is provided on the buffer layer opposite the reflection layer. In some embodiments, the at least one Group VIII metal comprises Ru and, in other embodiments, at least a portion of the buffer layer comprising Ru is less than about 3 nm thick. In still other embodiments, the Group VIII metal comprises at least one of Pt, Ir and Pd. Moreover, in some embodiments, the first and second materials may comprise Mo and Si.
Other embodiments of the invention include a stress relaxing layer between the substrate and the reflection layer. The stress relaxing layer can offset or reduce the compressive or tensile stress that is created in the reflection layer, and thereby reduce or eliminate curving of the reflection photomask.
In some embodiments, the predetermined pattern comprises first regions comprising the material that is configured to absorb extreme ultraviolet rays therein, and second regions that are free of the material that is configured to absorb extreme ultraviolet rays therein. In other embodiments, the buffer layer is thinner beneath the second regions than beneath the first regions. In yet other embodiments, the buffer layer comprises a patterned buffer layer that is patterned in the predetermined pattern. In still other embodiments, the buffer layer is a first buffer layer and the reflection photomask further comprises a second buffer layer between the first buffer layer and the absorber pattern, and that is patterned in the predetermined pattern. The first buffer layer can be thinner beneath the second regions than beneath the first regions.
Reflection photomasks may be fabricated, according to embodiments of the invention, by forming a plurality of alternating films comprising first and second materials on a substrate. A layer comprising at least one Group VIII metal is formed on the plurality of alternating films comprising first and second materials, opposite the substrate. A layer comprising material that is configured to absorb extreme ultraviolet rays therein is formed on the layer comprising at least one Group VIII metal, opposite the plurality of alternating films comprising first and second materials. Finally, the layer comprising material that is configured to absorb extreme ultraviolet rays is patterned. The composition and thickness of these regions may be as was described above. Moreover, in some embodiments, the layer comprising at least one Group VIII metal also is patterned with the predetermined pattern, such that the layer comprising at least one Group VIII metal is thinner beneath the second regions than beneath the first regions. In other embodiments, the layer comprising at least one Group VIII metal is patterned with the predetermined pattern, to remove the layer comprising at least one Group VIII metal beneath the second regions.
Finally, integrated circuits may be fabricated, according to embodiments of the invention, by exposing an integrated circuit to patterned extreme ultraviolet radiation, by reflecting the extreme ultraviolet radiation from a reflection photomask that can be configured according to any of the above-described embodiments of the invention and/or may be fabricated according to any of the above-described embodiments of the invention.